1. Field of the Invention
This invention relates to a low-cost, multiple-drive, data-storage system. More particularly, it relates to such a data-storage system comprising a controller that preferably is incorporated within a fixed-media disk drive and that decodes commands provided by a host computer to control both the fixed-media disk drive and a removable-media, optical-disk, disk drive.
2. Description of the Prior Art
Price competition has long been intense among manufacturers of various kinds of mass-market computer equipment. Such competition began to intensify in the early 1980's as desktop personal computers ("PC's") became popular. Throughout the 1980's and into the 1990's, such competition has remained relentless in the market for these desktop PC's, and the later-commercialized PC's such as laptops, and notebooks. Each of the foregoing PC's and each other programmable product that contains a central processing unit ("CPU"), a random access memory (RAM), and an input/output ("I/O") interface is referred to herein as a "host."
In the market for peripherals, such price competition has been and continues to be at least as intense as the price competition in the market for hosts. This is particularly true for products containing or consisting of drive mechanisms; such as small form factor fixed-media disk drives, and small form factor removable-media disk drives including floppy-disk disk drives and optical-disk disk drives. As used herein, the term "disk mechanism" applies equally to each of a variety of products, including "OEM-level" products (i.e., products which are generally sold only at the original equipment manufacturer ("OEM") level) and "retail-level" products (products which are sold at the retail level). One type of OEM-level, disk mechanism is interchangeably called a "head disk assembly" or an "HDA." One type of retail-level product that contains a disk mechanism is interchangeably referred to as a "fixed disk drive" or "hard disk drive," and generally includes a HDA and a controller for it. One type of OEM-level, removable-media disk mechanism into which an optical disk can be loaded is generally referred to herein as a "player mechanism"; one type of retail-level, removable-media product containing a disk mechanism, referred to as an "optical-disk disk drive," includes such a player mechanism and a controller for it. Each of these OEM-level and retail-level products and each other product that includes a housing containing a disk-supporting spindle, a spindle motor, a transducer, and a transducer-supporting actuator assembly, arranged to provide for reading data from at least one rotating disk, is within the scope of the term "disk mechanism," as used herein.
Reducing manufacturing cost to be less than those of competitors is generally a condition precedent to a manufacturer having its products enjoy commercial success in these markets. A reduction in either the number or cost of components can be quite significant to overall manufacturing costs, and accordingly extensive research and development efforts have been continuously expended by essentially all major manufacturers in this broad market with the common goal being to design and develop products incorporating fewer and less costly components.
One factor that has enabled computer-equipment manufacturers to reduce the number of components in their products is that semiconductor-fabrication technology has made it practical to combine many separate circuit structures into a single component; i.e., an integrated circuit ("IC"). This type of cost-reduction approach, involving combining of components, has occurred with great frequency in recent years. Another type of cost-reduction approach, involving integration of products, is much more rare. This cost-reduction approach is exemplified by a historical development in multiple-drive, data-storage systems.
In the early 1980's, a typical multiple-drive, data-storage system for a host such as a desktop PC included a so-called "storage board," and at least two so-called "dumb" magnetic disk drives. In such a data storage system, one of the two drives used floppy disks (i.e., removable media), and the other used built-in disks generally having higher capacity than a single floppy disk. Such a storage board generally included host-interface controller circuitry for interfacing the data-storage system to an I/O bus in the host. The host-interface controller circuitry operates in accordance with the protocol used for communication via the host I/O bus. Generally, such a storage board also includes a microprocessor, various general-purpose IC's such as memory circuits defining read-only memory ("ROM") and random-access memory ("RAM"), and various application-specific integrated circuits ("ASIC's"). These ASIC's include IC's that define a "channel" for performing functions involved in timing control needed for reading and writing data, circuits for implementing the host interface circuitry, and circuits for providing multiple peripheral-interface controllers for interfacing to a floppy disk drive and to a "dumb" fixed-disk drive conforming to the ST506 standard.
During the 1980's, the capacity and performance requirements for fixed-media disk drives increased, and "smarter" fixed-media, ST506 disk drives became commercially available. Such a "smarter" fixed-media ST506 disk drive includes a microprocessor and a memory for storing firmware, etc., for the microprocessor.
By the late-1980's, such multiple-drive, data-storage systems had been improved, and reduced in cost, by introduction of the intelligent fixed-disk drives referred to as "IDE drives" (The term "IDE" is an acronym for "Integrated Drive Electronics," and the term "IDE interface" is used interchangeably with interfaces defined in certain "ATA" specifications discussed below.) An IDE drive generally includes an HDA and a controller having an intelligent interface for communicating with a host computer and a low-level interface for communicating with the HDA. In contrast to the combination of two separate products, a "storage board" having its own microprocessor, and an ST506 drive also having its own microprocessor, the controller within an IDE drive generally includes a microprocessor that performs most if not all of the functions performed by the two microprocessors in the older storage-board based systems. This and other reductions in the number of components has contributed significantly to lower manufacturing costs, and has been accompanied by various performance improvements. One such performance improvement that accompanied the introduction of IDE drives involves caches in such drives. Nevertheless, the need for further cost reductions, particularly when combined with performance improvement, continues unabated. As for performance improvement, a need continues to exist for an improved architecture for allowing independent drives to operate concurrently (i.e., in a time-overlapped manner). Furthermore, a problem that has not been solved since the introduction of the intelligent disk drives relates to physical loading (current loading, capacitance loading, etc.) of the host I/O bus. In storage-board based systems, the drives themselves did not add physical loading to the host I/O bus; rather, only a storage board added such physical loading, and multiple drives could be used without adding to the physical loading of the host I/O bus. However, present multiple-drive systems entail multiple physical loads of the host I/O bus.
It is becoming increasingly common for a host to be equipped with a removable-media, optical-disk, disk drive. It is particularly common for such a disk drive to accept a so-called "compact disk" ("CD"). One type of CD is a "CD ROM" and a compatible drive is called a "CD ROM disk drive." A retail-level CD ROM disk drive includes a controller having an intelligent interface for communicating with a host computer. The intelligent interface may be a SCSI interface ("SCSI" is an acronym for Small Computer System Interface) or an IDE interface. The controller also includes circuitry for controlling the player mechanism. The player mechanism itself comprises a housing that opens to provide for loading an optical disk, a spindle for supporting the loaded optical disk, a spindle motor for rotating the spindle-supported optical disk, an optical-to-electrical transducer, and an electrically-controllable positioning structure for positioning the transducer relative to the rotating optical disk.
Whereas a typical magnetic floppy disk is capable of storing in the range of approximately one megabyte (1 MB), a typical CD ROM disk is capable of storing in the range of approximately 600 megabytes (600 MB). The ability of CD ROM disks to provide 600 megabytes or greater of digital audio, video, or other data in a transportable optically readable reflective disk has advantages over the lower capacity floppy disks, particularly for audio and video storage applications, including multimedia.
In addition to CD ROM disks and compatible drives (i.e., CD ROM disk drives), other types of optical disks and compatible drives include audio compact disks and compatible drives (generally called CD players) which were introduced commercially in the early 1980s. This original type of CD technology is typically referred to as CD-DA (Digital Audio) to distinguish it from the alternate versions of CD which have subsequently become available.
Commercially available CD ROM disk drives incorporate the same basic player mechanism as a CD-DA player but in addition incorporate decoding, error correction and other circuitry for reading data other than audio from the disk surface. As indicated by the name CD ROM, the data stored in this manner are readable only. In addition, extensions of the basic CD ROM technology have become available including CD-I (Interactive), CD-XA for Extended Architecture, CD-R or CD-Recordable, also known as CD-WO (Write Once), and CD-MO (Magneto Optical, a recordable form of CD). Currently, such CD variations are typically provided in form factors compatible with 120 mm optical disks as well as form factors compatible with 80 and 64 mm optical disks. Recently, a CD-MO, 64 mm disk format has been introduced by Sony that is referred to as CD minidisc or CD-MD.
Although some of these CD technologies have overcome the inability to write data onto the more conventional CD-DA or CD ROM type of optical disk, and although all provide for removable optical disk media, nonetheless such CD technologies have disadvantages. In particular, they are all characterized by a relatively slow access speed and data-transfer rate compared to fixed-media disk drives. This relative slowness of reading data from a CD creates very noticeable delays where the host must repeatedly go to the CD for data. This is particularly the case where applications, such as multimedia, requiring large amounts of data to be frequently transferred from permanent storage into working memory are being run on the host. Additionally, problems arise with "blocking accesses," particularly in relatively low-cost implementations such as those based on the IDE interface. For example, while the host is communicating with a CD ROM disk drive via the IDE bus, the host is blocked from communicating with a fixed-media disk drive that is connected to the common IDE interface. This blocking of the host prevents the host from taking advantage of the CD latency period to perform other tasks.
Commercially available multiple-drive systems incorporating both a fixed-media drive and removable-media, optical-disk, disk drive have a significant cost disadvantage. In such a typical commercially available system, the component count is quite high. Typically, each such drive has a host-interface controller; each has at least one microprocessor and an associated ROM storing firmware for programmably controlling the microprocessor; each has channel circuitry for processing data subject to correction by error-correcting means; each generally has buffer RAM and an associated buffer-manager circuitry. In addition to having such a high component count, such a commercially available multiple-drive storage system may, as discussed above, lack needed performance features such as concurrency of operations, and may suffer from blocking in the I/O path supporting the CD player during the CD latency period.
In summary, a need presently exists for a way to enhance the efficiency of a multiple-drive system employing both a fixed-media disk drive and a removable-media, optical-disk drive. Further, a need exists for a way to reduce the cost and space associated with such a multiple-drive system.